1. Field of the Invention
The present invention relates to a rolling mill for rolling a plate, and more particularly to a plate rolling mill using work rolls of small diameters and suitable for rolling a hard or ultra-thin strip.
2. Description of the Related Art
In such a rolling mill, using work rolls of smaller diameters provides a larger rolling limit (i.e., enables a plate to be rolled more thinly). For that reason, work rolls of small diameters have been heretofore used for rolling a hard or ultra-thin strip of, e.g., stainless steel. With a decrease in diameter of the work rolls, however, the torsional strength of the rolls themselves lowers inevitably, and a torque required for rolling cannot be applied to the work rolls in some cases. It is hence general that when using work rolls of small diameters, other rolls (for example, intermediate rolls) than the work rolls are rendered to operate as drive rolls.
In the above mill structure, the work rolls are each subjected during the rolling operation to a driving tangential force from a roll (for example, an intermediate roll) contacting with the work roll, and a front tension and a back tension from a plate under rolling. These force and tensions are all forces acting on the work roll in the horizontal direction (referred to as horizontal forces hereinafter). On the other hand, the smaller the diameter of the work roll, the smaller is the bending rigidity of the roll itself. Accordingly, the work roll undergoes deflection in a horizontal plane due to the horizontal forces.
The horizontal deflection causes a more marked disturbance in shape (flatness) of a plate under rolling. Also, when upper and lower work rolls deflect in opposite directions (one deflecting toward the incoming side and the other deflecting toward the outgoing side), central portions of upper and lower work rolls are subjected to forces acting in directions away from each other, thus accelerating the deflections of the work rolls in the opposite directions. In that case, if an excessively large rolling load is applied, it would be hard to surely prevent breakage of the rolls. The rolling load cannot be therefore so increased.
To cope with the problem mentioned above, there have been developed cluster-mill type rolling mills, including a Sendzimir mill, as well as a rolling mill provided with a horizontal deflection preventing mechanism wherein barrel portions of work rolls are supported horizontally by support rolls, as disclosed in JP,A,60-18206, for example. In these rolling mills, however, since the support roll is divided in the direction of length of the roll barrel, another problem occurs in that the surface properties of the plate being deteriorate due to mark transfer made by the divided support rolls.
For solving the above problem, JP,A,2-147108, for example, discloses a rolling mill wherein barrel portions of work rolls are supported horizontally by not-divided support rolls, and barrel portions of the support rolls are supported by hydrostatic pressure bearings, thereby suppressing deflections of the work rolls.
However, the rolling mill disclosed in JP,A,2-147108 accompanies the following problems.
In the disclosed rolling mill, rolling of a sheet is usually started with procedures below.
(1) A sheet to be rolled is threaded between the work rolls which are in a state moved away from the pass line (thereafter the sheet is held standstill);
(2) The work rolls are tightened to press the sheet under a predetermined load;
(3) A front tension and a back tension are applied to the sheet; and
(4) Intermediate rolls are rotated to drive the work rolls to start the rolling of the sheet.
As is apparent from the above procedures (1) to (4), in the state immediately before the start of the rolling (step (4)), a driving tangential force does not yet act on the work roll. At the same time as when the rolling starts, the driving tangential force generates and acts on the work roll abruptly. Because the rolling operation begins in such a discontinuous condition, a force tending to deflect the work roll to a larger extent generates transiently and a horizontal force imposed on the hydrostatic pressure bearing increases immediately after the start of the rolling.
With the hydrostatic pressure bearing constructed so as to float the work roll under hydrostatic pressure of a fluid (e.g., oil) and support it in a non-contact manner, the amount of floating of the roll (i.e., the gap between the roll and the hydrostatic pressure bearing) is momentarily reduced upon the generation of the above transient horizontal force. Also, at the moment when the roll starts rotating, the tensions etc. are apt to be unstable. For these reasons, it is hard to surely prevent the roll and the hydrostatic pressure bearing from being damaged upon contact with each other.
If the roll is damaged, a resulting scratch on the roll would be transferred to the surface of a sheet being rolled, and the rolled sheet would be a failed product. Therefore, the damaged roll and hydrostatic pressure bearing must be totally replaced. This may raise problems of reducing productivity and lowering yield.
As a method for avoiding the above problems, it is conceivable to apply a smaller initial tightening load to reduce a force imposed on the hydrostatic pressure bearing, and then to further tighten the roll to a predetermined load after the roll has rotated. With this method, however, a problem still remains in that the rolled sheet does not have a predetermined thickness immediately after the start of the rolling, and hence yield lowers.
Another conceivable method is to employ a resilient means, such as a spring, to adjust the distance between the roll and the hydrostatic pressure bearing as disclosed in JP,A,61-193704, for example. However, a resilient means has such a property that as an applied force increases, the resilient means deforms to a large extent. Accordingly, the provision of the resilient means is not sufficient to always maintain the distance between the roll and the hydrostatic pressure bearing to be not smaller than a certain value, and to surely prevent the roll and the hydrostatic pressure bearing from being damaged upon contact with each other.
With the view of solving the above problems in the related art, an object of the present invention is to provide a plate rolling mill which can always maintain a distance between a roll and a hydrostatic pressure bearing even in a transient state before and after the start of rolling, thereby sufficiently and surely preventing damage of those components upon contact with each other, and which can avoid a lowering of yield.
(1) To achieve the above object, according to the present invention, in a plate rolling mill comprising upper and lower work rolls, and hydrostatic pressure bearings for supporting barrel portions of the work rolls or barrel portions of support rolls in a non-contact manner with fluid pressure substantially along the horizontal direction, the support rolls supporting the work rolls substantially along the horizontal direction, the plate rolling mill further comprises stopper means for preventing gaps between the hydrostatic pressure bearings and the work rolls or the support rolls supported by the hydrostatic pressure bearings from becoming lower than a predetermined value.
With the above features, even when a force tending to deflect the work roll to a larger extent generates transiently immediately after the start of rolling to increase a horizontal force exerted on the hydrostatic pressure bearing supporting the work roll (or the support roll supporting it), and the gap between the hydrostatic pressure bearing and the roll (i.e., the amount of floating of the roll) is going to momentarily reduce, the gap can be prevented from becoming lower than the predetermined value. Accordingly, the gaps between the hydrostatic pressure bearings and the work rolls (or the support rolls) can be always maintained to be not smaller than the predetermined value. It is hence possible to sufficiently and surely prevent those components from being damaged upon contact with each other, and to avoid a lowering of yield.
(2) In the above (1), preferably, the stopper means are roller means provided in contact with the work rolls or the support rolls substantially in the horizontal direction.
(3) In the above (2), preferably, the hydrostatic pressure bearings support the barrel portions of the support rolls in a non-contact manner, and the roller means are provided in contact with the work rolls substantially in the horizontal direction.
(4) In the above (2), preferably, the hydrostatic pressure bearings support the barrel portions of the work rolls in a non-contact manner, and the roller means are provided in contact with the work rolls substantially in the horizontal direction.
(5) In the above (2), preferably, the hydrostatic pressure bearings support the barrel portions of the support rolls in a non-contact manner, and the roller means are provided in contact with the support rolls substantially in the horizontal direction.
(6) In the above (5), preferably, each of the support rolls includes a first support roll in direct contact with corresponding one of the work rolls for supporting the same substantially along the horizontal direction, and second support rolls in contact with the first support roll for supporting the same at plural points in the vertical direction, each of the hydrostatic pressure bearings supports the barrel portions of the second support rolls in a non-contact manner, and each of the roller means is provided in contact with the first support roll substantially in the horizontal direction.
(7) In the above (2), preferably, each of the roller means is provided in contact with corresponding one of the work rolls or the support rolls at plural points in the vertical direction.
(8) In the above (2), preferably, the roller means are fixed to beams to which the hydrostatic pressure bearings are connected.
(9) In the above (2), preferably, the roller means are connected to a housing of the plate rolling mill, and the plate rolling mill further comprises roller advancing/-retracting means for moving the roller means back and forth with respect to the housing.
(10) In the above (1), preferably, the stopper means are block members fixed to the hydrostatic pressure bearings so as to project toward the work rolls or the support rolls.
(11) In the above (2) or (10), preferably, the roller means or the block members are in contact with the work rolls or the support rolls at positions axially outside an area corresponding to a maximum width of plates to be rolled.
With the above features, the surface properties of the rolled plate can be kept from deteriorating due to mark transfer made upon contact between the rolls and the plate.
(12) Also, to achieve the above object, according to the present invention, in a plate rolling mill comprising upper and lower work rolls, and hydrostatic pressure bearings for supporting barrel portions of the work rolls or barrel portions of support rolls in a non-contact manner with fluid pressure substantially along the horizontal direction, the support rolls supporting the work rolls substantially along the horizontal direction, the plate rolling mill further comprises holding means for holding gaps between the hydrostatic pressure bearings and the work rolls or the support rolls supported by the hydrostatic pressure bearings at a predetermined value.
With the above features, the gaps between the hydrostatic pressure bearings and the work rolls (or the support rolls) are held at the predetermined value by the holding means. Therefore, even when a force tending to deflect the work roll to a larger extent generates transiently immediately after the start of rolling to increase a horizontal force exerted on the hydrostatic pressure bearing supporting the work roll (or the support roll supporting it), the gap between the hydrostatic pressure bearing and the work roll (or the support roll) can be always maintained at the predetermined value regardless of an increase of the horizontal force. It is hence possible to sufficiently and surely prevent those components from being damaged upon contact with each other, and to avoid a lowering of yield.
(13) In the above (12), preferably, the holding means include chocks for rotatably supporting the work rolls or the support rolls.
(14) In the above (13), preferably, the chocks are connected to beams to which the hydrostatic pressure bearings are fixed.
(15) In the above (13), preferably, the chocks are connected to a housing of the plate rolling mill, and the plate rolling mill further comprises chock advancing/-retracting means for moving the chocks back and forth with respect to the housing.
(16) In the above (1) or (12), preferably, each of the hydrostatic pressure bearings has an axial width not smaller than a maximum width of plates to be rolled.
(17) In the above (1) or (12), preferably, the plate rolling mill further comprises detecting means for detecting the gaps between the hydrostatic pressure bearings and the work rolls or the support rolls, and control means for controlling fluid pressures at the hydrostatic pressure bearings in accordance with results detected by the detecting means.
(18) Further, to achieve the above object, according to the present invention, in a plate rolling mill comprising upper and lower work rolls, and hydrostatic pressure bearings for supporting barrel portions of the work rolls or barrel portions of support rolls in a non-contact manner with fluid pressure substantially along the horizontal direction, the support rolls supporting the work rolls substantially along the horizontal direction, the plate rolling mill further comprises means for maintaining gaps between the hydrostatic pressure bearings and the work rolls or the support rolls supported by the hydrostatic pressure bearings to be not smaller than a predetermined value.
(19) Further, to achieve the above object, according to the present invention, in a plate rolling mill comprising upper and lower work rolls for rolling a plate, support rolls for supporting said work rolls substantially along the horizontal direction, hydrostatic pressure bearings for supporting barrel portions of said support rolls with fluid pressure substantially along the horizontal direction, and members disposed on both sides of said support rolls in the axial direction thereof for setting positions of said work rolls to predetermined positions substantially in the horizontal direction.
(20) In the above (19), preferably, the plate rolling mill further comprises, support beams for supporting said hydrostatic pressure bearings, and moving devices capable of moving said hydrostatic pressure bearings through said support beams substantially in the horizontal direction, wherein one of said members for setting positions of said work rolls to predetermined positions substantially in the horizontal direction is mounted to corresponding one of said support beams and comprises a rotating roller or a block.
(21) Further, to achieve the above object, according to the present invention, in a plate rolling mill comprising upper and lower work rolls for rolling a plate,support rolls for supporting said work rolls substantially along the horizontal direction, hydrostatic pressure bearings for supporting barrel portions of said support rolls with fluid pressure substantially along the horizontal direction, detecting devices for detecting gaps between said hydrostatic pressure bearings and said work rolls or said support rolls, and a control unit for controlling fluid pressures at said hydrostatic pressure bearings in accordance with values detected by said detecting devices.
(22) Further, to achieve the above object, according to the present invention, in a rolling method comprising the steps of supporting upper and lower work rolls for rolling a plate by support rolls substantially along the horizontal direction, supporting barrel portions of said support rolls with fluid pressure substantially along the horizontal direction under supply of a fluid, and pressing said work rolls on both sides of said support rolls in the axial direction thereof for setting positions of said work rolls to predetermined positions substantially in the horizontal direction before and after the start of rolling.
(23) Further, to achieve the above object, according to the present invention, in a rolling method comprising the steps of supporting upper and lower work rolls for rolling a plate by support rolls substantially along the horizontal direction, supporting barrel portions of said support rolls with fluid pressure substantially along the horizontal direction under supply of a fluid, and pressing said work rolls at positions axially outside an area corresponding to a maximum width of plates to be rolled for setting positions of said work rolls to predetermined positions substantially in the horizontal direction before and after the start of rolling.
(24) Further, to achieve the above object, according to the present invention, in a rolling method comprising the steps of supporting upper and lower work rolls for rolling a plate by support rolls substantially along the horizontal direction, supporting barrel portions of said support rolls with fluid pressure substantially along the horizontal direction under supply of a fluid, detecting gaps between said hydrostatic pressure bearings and said work rolls or said support rolls, and controlling fluid pressures at said hydrostatic pressure bearings in accordance with detected gap values.